spec-and-tsan #1

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dtourolle merged 4 commits from spec-and-tsan into master 2026-07-17 18:11:51 +00:00

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dtourolle commented 2026-07-14 17:57:11 +00:00

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dtourolle added 3 commits 2026-07-14 17:57:12 +00:00

test: add ThreadSanitizer verification for lock-free Channel<T> ... 50032ffce3

Add a contended SPSC stress suite (tests/test_channel_stress.cpp) that
actually exercises the ring's memory-ordering pairing and spin/futex/
lost-wakeup logic, plus the CMake and CI plumbing to run it under TSan:

- KPN_SANITIZER cache var + kpn_sanitizer_flags() helper (no-op when unset)
- kpn_tests_stress executable, labelled "stress" for CTest
- reusable tsan.yaml workflow (gcc:14 builder image, already ships libtsan)
- ci.yaml gains a tsan job on the same code/dockerfile triggers as test

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs: rewrite SPEC.md to match the implemented library ... 001e192bb3

The spec had drifted far from the code. Key corrections:

- Execution model is reactive (PoolNode submits fire_once() to a
  ThreadPool when inputs are ready), not one blocking thread per node
- Channel<T> is a lock-free SPSC ring buffer (atomic wait/notify +
  spin-before-sleep), not a mutex+CV queue
- Remove latch<> ports (never implemented)
- NodeErrorHandler returns bool (skip vs stop); per-node
- Document new subsystems: scheduler, InterruptNode, Router/FilterNode,
  MainThreadNode, SharedResource, DebugHub, diagnostics/stats layer
- Update StaticNetwork, Python auto_bind layer, examples 01-16

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

fix: deliver EOF sentinel only when the ring is freshly empty ... bceccc3406

Channel<T>::pop() surfaced the out-of-band sentinel from its empty branch
using the tail_ snapshot taken at the top of the loop. Under contention the
producer can push more values *and* the sentinel in the window between that
snapshot and take_sentinel(), so pop() could return the sentinel while real
values still sat in the ring — the sentinel jumping ahead of values pushed
before it. No value was lost (a consumer that keeps draining still receives
them, and approx_size() keeps counting them so a PoolNode reschedules), but a
consumer treating the sentinel as a hard "last message" barrier would act on
EOF early.

Re-confirm emptiness against a fresh tail_ load before taking the sentinel.
Costs one acquire-load on the empty-ring path only; never runs in steady
state. The spin and post-spin takes already reload tail_ on the line above
them; try_pop_now() already reads tail_ fresh in the same branch — both were
correct and are unchanged.

The two sentinel stress cases now assert the strict "sentinel is last, after
every value" ordering (previously relaxed to avoid the flake this fixes).
Verified TSan-clean (2606 assertions, no data races) over repeated runs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dtourolle force-pushed spec-and-tsan from bceccc3406 to a0c4bf580e 2026-07-14 21:17:03 +00:00 Compare

dtourolle added 1 commit 2026-07-17 18:02:01 +00:00

ci: fix TSan aborting at init on the nested-LXC runner ... ec19137ed9

The ThreadSanitizer job runs on Docker nested in an unprivileged LXC
container, whose kernel randomizes mmap addresses beyond the range TSan's
fixed shadow mapping expects. TSan aborted at init with "unexpected memory
mapping" before any test ran.

Disable ASLR per-process with `setarch -R`, which needs the personality(2)
syscall that Docker's default seccomp profile blocks; seccomp=unconfined on
the container permits it. Verified on the runner that both are required:
setarch -R alone gets EPERM, seccomp alone still aborts, both together run
clean. Scoped to the tsan job, which runs only our own test binaries.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dtourolle merged commit 5ecf3cde4f into master 2026-07-17 18:11:51 +00:00

dtourolle referenced this issue from a commit 2026-07-17 18:11:52 +00:00

Merge pull request 'spec-and-tsan' (#1) from spec-and-tsan into master

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Reference: dtourolle/KPN#1